An Outline of Anaesthetic Procedures

There has been a lot of progress in the department of anesthetics since doctors performed the first etherisations in the 19th century. In the following article, you will gain an overview of the popular anesthetic procedures, their indications and side effects – just as important in the clinical context as for the examination.

General vs. Local Anesthesia

General anesthesia induces unconsciousness and affects the pain perception of the brain. This form of anesthesia is used in operations that are not bearable for patients when they are awake.

Local- or regional anesthesia prevents the transmission of pain from a certain point in the body to the brain. Specific peripheral nerves get blocked with a local anesthetic; sensations from other areas of the body are maintained. The patient is awake and can react adequately.

General Anesthesia

The goal of general anesthesia is to bring the patient into a temporary state of:

Normally, general anesthesia is initiated intravenously and continued via an inhaled anesthetic (balanced anesthesia) or an intravenous anesthetic (total intravenous anesthesia, TIVA). Both procedures can be viewed as equally effective in principle.

Note: Patients with an increased risk of aspiration complications always need an intravenously, not inhaled initiated anesthesia. Pregnant patients or patients with ileus, adiposity or insufficient soberness are regarded as a particular risk group for risk of aspiration.

Respiratory System Protection

The medications that are used for general anesthesia lead to a respiratory depression. There are various procedures with different indications for artificial respiration.

Face mask: a least invasive procedure used for very short interventions in supine or lithotomy position. Some of the disadvantages of this procedure are the lack of separation of respiratory system and gastrointestinal tract.

Laryngeal mask: this mildly invasive procedure makes use of a lens tube with an inflatable mask that is inserted in the throat up to the larynx. The air filled mask nestles up against the pharynx and around the epiglottis. The mask does not offer a safe aspiration protection, which is why artificial respiration via a larynx mask may only be applied to sober patients. The larynx mask is used for surgical interventions on body surface or extremities, ENT- and eye surgery as well as emergency cesarean-section.

Endotracheal intubation: Artificial respiration with an endotracheal tube is the safest and most invasive technique. The tube is inserted either through the mouth (orotracheal intubation) or the nose (nasotracheal intubation) and ends in the trachea via the glottis. One of the advantages of the endotracheal intubation is that the patient is protected from aspiration of foreign bodies (saliva, blood, stomach contents). The patient can be attached to a respirator.

Procedure

After induction with an inhaled or IV analgesic (Propofol), anesthesia can be maintained with inhaled anesthetics such as Isoflurane, Sevoflurane or Desflurane, which is added to a gas mixture consisting of O2 and ambient air or nitrous oxide (N2O).

Balanced Anesthesia Procedures

Additionally, short- and long-term effective opioids can be added to the analgesic effect. The combination of inhaled narcotics and IV opioids is known as balanced anesthesia. It represents the most common form of anesthesia and is characterized by good control of anesthesia.

Evaluation of the Narcosis

Blood pressure, spontaneous breathing, and/or muscle contractions can hint at the level of a patient’s anesthesia. Shallow anesthesia can manifest as increased blood pressure and heart rate, spontaneous respiration, and defensive bodily movements. The reason for this is the release of catecholamine due to pain.

A good narcosis management is marked by the fact that the narcosis is being held as shallow as possible without displaying the symptoms of a too shallow narcosis mentioned above. To achieve this state, it is important to have knowledge about the exact course of the operation and to closely observe it in order to adjust the depth of narcosis. As the inhaled anesthetic’s onset of action occurs out of phase, the anesthesiologist needs to know the course of the operation in order to adjust the alveolar concentration of the anesthetics to the surgical stimulation.

TIVA – Total Intravenous Anesthesia

General anesthesia can also be conducted with purely intravenously administered substances. This case is known as total intravenous anesthesia (TIVA).

Here, no inhaled anesthetic is being used. Instead, an intravenously injected hypnotic (e.g. Propofol) in combination with an opioid (e.g. Remifentanil, which has a very short half-life) and muscle relaxer are applied. Artificial respiration of the patient is carried out through an O2-mixture.

The goal of the TIVA procedure is to quickly reach a Steady State with constant plasma levels of the drugs. The depth of the narcosis should be directly adjusted to the surgical phase, which is why substances with a quick elimination (e.g. the combination of Propofol/Remifentanil) are used.

Indications of TIVA

The TIVA is especially handy for short surgical interventions with a consistent depth of narcosis (e.g. minimally invasive surgery, ambulant anesthesia). When anamnestic cues for malignant hyperthermia are present, a TIVA without the usage of trigger substances may be conducted.

Advantages of TIVA

The patients wake up quickly after the operation, which is why total intravenous anesthesia is preferred for ambulatory/outpatient surgery. Also, Propofol has an antiemetic effect, so postoperative nausea occurs less frequent.

Regional Anesthesia

Pain transfer from a specific body region up to the brain is selectively prevented in regional anesthesia. In this procedure, the respective peripheral nerves are selectively disabled using a localanesthetic. Local anesthetics are drugs that prevent the depolarization of nerve cells by blocking their sodium channels. Due to membranestabilization, no depolarization or transmission of impulses can occur. Local anesthetics are injected around the peripheral nerves and then diffuse to the nerves.

Complications of Local Anesthesia

The drugs can, however, also diffuse into the bloodstream and cause side effects in the brain and the heart. At high concentrations, local anesthetics can surge e.g. in the brain and unfold a toxic effect by creating an unwanted stabilization of the membrane there.

The heart’s conduction system can be negatively influenced by a toxic concentration of local anesthetic. This leads to a decreased heart rate, AV blockage, a decrease in heart strength and blood pressure as well as a possible cardiac arrest.

Anaphylactic reactions to local anesthetics are also possible, which may express themselves through urticaria, an asthma attack or a decline in blood pressure up to an anaphylactic shock.

Note: An accidental intravenous injection of the local anesthetic must be avoided. Repetitive aspiration checks during the administration should, therefore, be conducted. The injection should be given slowly and be divided into multiple doses.

Advantages of Local Anesthesia

Altogether, local anesthesia presents lower strain for the patient, fewer complications, and fewer medical attendants during and after the operation.

Image: “Left: puncture of the axillary block via the axillary artery. Right: the course of the artery and nerve, place of elimination.” by David Shankbone. License: CC BY-SA 3.0

Local And Regional Anesthesia Procedures

Local anesthesia

Surface anesthesia (mucosal anesthesia): A local anesthetic is applied onto the mucous membrane area, causing the sensitive nerve ends lying there to be blocked. Application: e.g. before the male urethral catheterization in form of a local anesthetic containing a lubricant, EMLA-crème for siting of peripheral venous aditus in child anesthesia.

Infiltration anesthesia: Local (intradermal, subcutaneous or intramuscular) injections of local anesthetics into the area of operation, blocking the sensitive nerve endings in this area. Application: e.g. for wound treatment. A local anesthetic with adrenaline supplementation may be used, which leads to a local vasoconstriction. This has the advantage of a slower resorption and an increased duration of action, while systematic-toxic side effects can be reduced.

Conduction and local anesthesia

Peripheral nerve block: inject close to the nerve to block sensation distal to an injection site.

Plexus block: same as a peripheral nerve block, but anesthetic is injected near the nerve plexus (i.e. brachial or lumbosacral) in order to block a larger area of the body.

Conduction anesthesia close to the spinal cord

Spinal anesthesia: Inserting local anesthetic into the spinal canal, enabling blockage of pain in the lower half of the body

Peridural/epidural anesthesia: The local anesthetic is being placed in the peridural area for the peridural anesthesia (PDA). The peridural area lies behind the ligamentum flavum of the spine and contains fat, connective tissue, and venous plexus. The dura mater is not damaged during the PDA.

Indications and Contraindications of Local Anesthesia

Advantage: the patient does not need to be under complete/general anesthesia.

Disadvantage: can be a time-consuming procedure and the long duration after surgery can hide nerve damage done during surgery.

Contraindications of regional pain blockage:

Local infection at the area of injection

Systemic infection

Clotting disturbances/anticoagulants

Allergy to local anesthetics or allergy of preservatives – methylparaben

Inflammable changes of lymph vessels or nodes in the area to be numbed (plexus brachialis blockage: Grope lymph nodes of axilla before!)

Procedures Close to the Spinal Cord

Spinal anesthesia: Placing the local anesthetic in the spinal canal and into the cerebral fluid interspaces makes it possible to block pain in the lower half of the body and is therefore used as an anesthetic for operations of legs, hips, abdomen and the groin area. Spinal anesthesia has also become the standard procedure with C-sections (section caesarea).

Peridural anesthesia (= epidural anesthesia): Injection of the local anesthetic in the epidural space around the dura mater (but not in the venous plexus). As opposed to spinal anesthesia, the dura mater does not get pierced. Theoretically, the PDA can be applied at any point on the spinal cord, as the dura does not get injured. A thoracic PDA demands highest caution and expertise due to the risk of injuring the spinal cord.

Procedure of Spinal Anesthesia

Spinal anesthesia may only be conducted below the third lumbar vertebra to avoid injury of the spinal cord (usually the spinal cord ends at L1/L2 under which the nerve fibres form the cauda equina, which easily dodge the incoming cannula).

Spinal puncture can be done in both sitting and procumbent patients. The patient’s posture is important – he/she needs to form a humpback (“arched back”) in order to enlarge the spaces between the spine.

The most widely used point of injection is positioned at L3/L4. The site is located at the level of the iliac crests.

The procedure of a spinal anesthesia:

Once disinfected, a sterile fenestrated drape may be affixed.

Skin and deeper structures are numbed with a local anesthetic.

A spinal needle is pierced through the ligament interspirale.

The thin spinal cannula may now be inserted through the guide cannula. The fibers of the dura mater are pushed apart by the spinal cannula’s polish if held correctly, instead of poking a hole in the dura mater. The dura perforation can often be felt as a small “click”. By removing the mandrin from the spinal cannula, one can make sure that the needle-syringe lies in the cerebral fluid interspaces: If it lies correctly, clear liquid will drop out of the cannula.

Now, the local anesthetic may be injected. A small amount of liquid should be aspirated beforehand to be absolutely sure that the tip of the needle is still in the correct cerebral fluid interspace.

After removing the cannula, the puncture site may be covered with a sterile bandage.

Possible Complications with Spinal Anesthesia

The liquid may flow through the hole in the dura from the spine into the peridural area. This results in losing a small amount of liquid, which may bear small displacements of the brain and spinal cord as consequence. Ultimately, a dragging pain at the meninges results, which probably leads to strong, mostly analgesic-incompatible headaches.

Therapy of post-puncture headache

Positioning the patient horizontally for the first 24 hours after the puncture can delay a post-spinal headache, but does not prevent them completely. Caffeine and theophylline may be administered. Usually, the headache wears off after a few days. If this does not happen, one can apply a peridural blood patch – the patient’s blood is gathered and injected into the peridural space at the point of puncture. The clotting blood seals the hole in the dura, which usually results in a quick improvement of symptoms.

Further possible complications

Hypotension (due to the quick onset of the sympathetic blockage),

Cranial nerve lesions (nervus abducens → double pictures),

Injuries of the spinal cord when punctuating too high, spinal anesthetic may rise up too high and inhibit the intercostal respiratory muscles and heart sympathetically,

Bacterial infection (→ meningitis),

Peridural hematoma (due to an injury of venous vessels in the peridural area, difficult to avoid) for existing clotting problems; In the worst case, a compression of the spinal cord up to paraplegic symptoms may result from the forming hematoma. Therefore, it is absolutely necessary to perform a prior anamnesis and a test of blood clotting and to check for possible clotting complications or medication that may interfere with clotting.

Note: A clotting test should be performed before local anesthesia near the spinal cord and plexus blockages. Quick-value (normal 70 – 130 %), INR (normal 0,85 – 1,15) and PTT should lie within normal parameters. The number of thrombocytes should not be lower than 100 000/mm3. Once lower molecular heparin has been added to the thromboprophylaxis, a security interval of 12 hours should adhere.

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